The invention relates to a thermostatic device with two operating thresholds so as to provide two ranges of regulation which can be activated selectively.
Such devices are of use particularly in the field of motor vehicles, to optimize the cooling of the vehicle engine according to the load thereon.
Conventionally, the liquid cooling circuit of internal combustion engines includes a system of pipes connecting the engine to a cooling radiator in which a thermostatic device is inserted. In the liquid bound for the engine, the proportion of so-called xe2x80x9ccoldxe2x80x9d liquid from the radiator and so-called xe2x80x9chotxe2x80x9d liquid which has not passed through this radiator is modified by the cooling circuit so as to supply the engine block with cooling liquid at one and the same, theoretically optimum, temperature regardless of the circumstances.
However, it has been found that at very high load, the engine xe2x80x9cheats upxe2x80x9d in such a way that maintaining the normally optimum temperature at the inlet to the engine leads to an internal temperature thereof which is likely to cause the engine to become damaged.
To avoid this drawback, a temperature lower than the normally optimum temperature is chosen as the liquid inlet temperature. However, at low load, which corresponds to the most frequent usage of the vehicle, the engine runs appreciably below the optimum temperature and the fuel consumption and pollution are increased.
With a view to overcoming this new drawback, the subject of document FR 93/11919 relates to a thermostatic device comprising a single thermostatic element which regulates the temperature by means of a valve and simply offsets the regulation range, when the engine is operating at full load, to then regulate to a lower temperature than the temperature which is optimum under normal conditions (generally approximately at half-load). To this end, the thermostatic element comprises an electrical heating element providing it with additional heating when an appropriately located probe detects that the engine is running near to full load. However, if the thermostatic element fails, it no longer fulfills its regulating function and the regulating valve remains closed, which very soon leads to engine damage.
With a view to avoiding such a drawback, the subjects of documents FR 85/15967 and U.S. Pat. No. 4,875,437 relate to a thermostatic device comprising a regulating element located in the cooling circuit and a heated offsetting element outside the cooling circuit and which is carried by a cap that closes the device and extends transversely to the axis or to the direction of movement of the moving part of the thermostatic element. By virtue of this design, if the heated offsetting element fails, there is still regulation although the offsetting element is subjected to the potentially unfavorable conditions of the surroundings external to the thermostatic device, particularly inclement weather if used on a vehicle. In addition, it is difficult to gain perfect control over the level of temperature of this element. Furthermore, the arrangement adopted does not allow the device to possibly have two ports aligned in the direction in which the axis of movement of the moving part of the regulating element extends, which is what it needs to have given the way in which it is fitted on certain engines.
In order to overcome these drawbacks and others which will be seen hereinafter, the invention relates to a thermostatic device with two levels of regulation. A fluid-metering moving assembly comprises at least one valve and is designed to move in a chamber which has a first fluid inlet port, a second fluid outlet port, and at least one third port, and at least one of these three ports is surrounded by a valve seat. The metering moving assembly is carried by part of a fluid-metering thermostatic element which can move with respect to another part of the thermostatic element, which part is arranged at least partially outside the chamber. The thermostatic device also includes a housing part in the form of a duct for the passage of cooling fluid, one end of which opens into the chamber via a valve seat surrounding one port of the chamber. The thermostatic device is further characterized in that it also includes a thermostatic element for adjusting the regulation threshold, and has a moving threshold-adjusting part equipped with a moving stop for the part of the metering thermostatic element which is outside the chamber. At least one region of the threshold-adjusting element comprises at least one portion of its fixed part, and at least its moving part extends into the cooling fluid duct The region contains heating means designed to be switched selectively into one of two temperature states such that in the higher temperature state, the distance between the moving stop and the seat via which the duct opens into the chamber, and thus the temperature for which this seat is opened by its valve, are respectively smaller and lower than in the other state.
Thus, with the thermostatic element sheltered from climatic uncertainties, reliable regulation is achieved, and regulation continues to be achieved even in the event of mechanical failure other, of course, than complete destruction of the device. In addition, by virtue of this design, the duct can, if necessary, be straight and connected to a pipe aligned with the direction of movement of the moving assembly. Furthermore, the threshold-adjusting element can itself be carried by a peripheral exterior wall of part of a housing, being partially housed therein. Thus, on the one hand, the dimensions of the device can be appreciably reduced and, on the other hand, any connecting wires there might be for connecting the electrical heating means to a source of power do not have to pass through a stuffing box. Also, the device is simple and quick to mount.
The device may in particular exhibit one or more of the following characteristics.
The threshold-adjusting thermostatic element comprises electrical heating means designed to be electrically connected to a control means comprising a source of electrical power that can be switched on and off selectively.
The source of electrical power can be switched on and off selectively so as to switch the threshold-adjusting thermostatic element into one of a heated state and of a non-heated or less-heated state. Therefore, when the threshold-adjusting element is heated, the distance between the moving stop and the duct-side port seat, and thus the temperature for which this seat is uncovered by its valve, are respectively smaller and lower than when it is not heated or is less heated.
The threshold-adjusting element extends entirely into the duct, and the exterior wall of the duct has a stuffing box passing through it The electrical wires for electrically connecting the heating means to control means comprising a source of electrical power that can be switched on and off, selectively, pass through the stuffing box.
The fixed part of the threshold-adjusting element passes through the exterior wall of the duct and extends in a direction perpendicular to the direction in which the moving part of the metering thermostatic element can move.
The fixed part of the threshold-adjusting element passes through the exterior wall of the duct and extends in a direction which is inclined with respect to the direction in which the moving part of the metering thermostatic element can move.
The fixed part of the threshold-adjusting element passes through the exterior wall of the duct and extends in the same direction as the direction in which the moving part of the metering thermostatic element can move.
The threshold-adjusting element comprises a fixed part, a portion of which extends approximately transversely into the internal space of the duct
The duct is centered on a longitudinal axis on which the valve seat via which one end of the duct opens into the chamber is centered. The moving part of the metering thermostatic element which carries the moving assembly comprising the valve for this seat can move in terms of translation along this axis.
The duct is bent, and the means of heating the threshold-adjusting element extends into the fixed part of this element, in the direction in which this fixed part passes through the exterior wall of the duct.
The means of heating the threshold-adjusting element extends in the direction in which the moving part of the metering thermostatic element can move.
The heating means comprises a wound electrical resistive element, and the electrical heating means comprises an electrical resistive element printed onto an insulating wafer. The electrical heating means also may comprise an electrical resistive element consisting of a resistive rod.
The heating means comprises an electrical resistive element housed in a compartment containing a mass of expanding wax of a housing belonging to the fixed part of the threshold-adjusting element.
The fixed part of the threshold-adjusting element comprises a housing which has a compartment containing a mass of expanding wax. The housing has, facing the seat, an opening which is closed off by a diaphragm.
The threshold-adjusting element comprises a diaphragm in the shape of a bell known as a xe2x80x9cbag diaphragmxe2x80x9d, or the threshold-adjusting element can comprise a flat diaphragm.
The duct comprises two abutting portions fixed together, and the facing respective mating surfaces of the abutting portions have cut-outs in which a region of the threshold-adjusting element is inserted.
The fluid-metering moving assembly comprises at least two valves, and at least two of the at least three ports are surrounded by respective seats for the two valves so that when any one of the valves leaves its seat and moves away from it, the other moves closer to its seat, possibly to the point of closing it off.
The electrical heating means is connected by electrical wires to a source of electrical power also connected to a temperature-detecting probe designed to detect the temperature of a liquid.
The electrical heating means is connected by electrical wires to a source of electrical power is also connected to a temperature-detecting probe designed to detect the temperature of a liquid and to an alarm so that when the probe detects a temperature at least equal to a predetermined safe temperature, the source of electrical power is switched on. Thus on the one hand, the adjusting element is electrically heated and the device regulates in a low range of temperatures and, on the other hand, the alarm is activated.
The chamber has an outlet port surrounded by a seat made in the duct for a valve, an outlet port possibly surrounded by a seat for a valve, and an inlet port.
The inlet port is an inlet port for hot liquid from an engine, for example, of a vehicle. The outlet ports are outlet ports for hot liquid designed to be connected respectively to an inlet of a cooling radiator and to an inlet of the engine, possibly via a circulating pump.
The chamber has an inlet port surrounded by a seat made in the duct for a valve, an inlet port possibly surrounded by a seat for a valve, and an outlet port.
The inlet port surrounded by a seat made in the duct is an inlet port for cold liquid designed to be connected to a cooling radiator, for example, of a vehicle. The other inlet port is an inlet port for hot liquid from an engine of the vehicle, and the outlet port is an outlet port for hot liquid or cold liquid or a mixture of hot liquid and cold liquid depending on the position of the metering thermostatic element.